1. Field of the Invention
The present invention generally relates to a development device; and a process cartridge and an image forming apparatus, such as, a copier, a printer, a facsimile machine, or a multifunction machine including at least two of these functions that includes a development device; and, more particular, to adjustment of the amount of two-component developer in the development device.
2. Description of the Background Art
Two-component developer consisting essentially of toner particles and carrier particles is widely used in image forming apparatuses such as photocopiers, facsimile machines, printers, or multifunction machines having several of those capabilities. Two-component development devices typically include a development roller (i.e., a developer bearer), multiple developer conveyance members to transport developer in the longitudinal direction of the development device, thereby forming a developer circulation path, and a developer regulator to adjust the amount of developer carried on the development roller upstream from a development range where the development roller faces an image bearer such as a photoreceptor.
For example, developer can be circulated unidirectionally in the following configurations. An interior of the development device containing the respective components is separated by a partition (i.e., an inner wall) into multiple compartments or conveyance channels, and the partition is absent at the both ends in the longitudinal direction, thus securing communication areas through which developer moves from one conveyance channel to another conveyance channel.
Fresh toner is supplied through a toner supply inlet to the two-component development device as the toner inside the development device is consumed in image development. The supplied toner is mixed with the developer in the development device by the developer conveyance member, such as a screw, serving as a developer supply member, and then the mixed developer is partly supplied to a circumferential surface of the development roller. While the development roller rotates, the developer regulator (e.g., a doctor blade) disposed facing the development roller adjusts the amount of the developer carried on the development roller, and then the toner in the two-component developer adheres to a latent image formed on the image bearer in the development range.
There are development devices in which two developer conveyance members (first and second developer conveyance members), respectively serving as the developer supply member and a developer collecting member, are arranged vertically, forming a developer circulation channel.
Arranging the multiple developer conveyance members vertically is widely used in tandem multicolor image forming apparatuses in which multiple development devices are arranged horizontally because this arrangement can make the development device horizontally compact. Compared with an arrangement in which multiple conveyance members are arranged in parallel horizontally, this arrangement can better inhibit the developer that has been used in image development from being supplied to the developer bearer, thus reducing unevenness in image density.
For example, the developer regulator may be disposed facing an upper circumferential surface of the developer bearer, and the developer supply member may be disposed above the developer collecting member across the partition.
Alternatively, for example, JP-H11-174810-A proposes a configuration in which the developer regulator faces a lower circumferential surface of the developer bearer, and the developer supply member (first conveyance member) is beneath the developer collecting member (second conveyance member) across the partition.
The first conveyance member (lower conveyance member) supplies developer from a first conveyance channel onto the development roller at a position corresponding to an attraction magnetic pole generated by a magnet roller provided inside the development roller while transporting the developer longitudinally. The second conveyance member receives developer separated from the development roller at a position corresponding to a release magnetic pole and transport the developer in a second conveyance channel in the direction opposite the direction in which the first conveyance member transports the developer.
The first and second conveyance channels communicate with each other through first and second communication openings. The amount of developer decreases downstream in the supply channel in the developer conveyance direction therein, whereas the amount of developer increases downstream in the collection channel in the developer conveyance direction therein.
The configuration proposed in JP-H11-174810-A can inhibit increases in the load to the driving system caused to bring up developer against the gravity on the downstream side in the direction in which developer is transported, compared with the former configuration.
Additionally, there are image forming apparatuses that offer selection of image formation modes for forming high-quality images, forming images on thicker paper, and the like. In addition to temperature and speed of image fixing, image formation speed may be changed depending on the image formation mode. For example, image formation speed is slowed down to form high-quality images or to form images on thicker paper. By contrast, image formation speed is increased to accelerate consecutive copying or first print time.
Changes in image formation speed can affect the balance of the amount of developer in the development device. For example, the amount of developer carried on the development bearer may be equalized by leveling off the height of developer carried, which depends on the screw pitch of the developer conveyance screw.